1. Field of the invention
The instant invention relates to an electromagnetic lock provided with a retractable sliding bolt for a swinging-type door, that is, a lock comprising a doubly-tapered bolt. The door is openable by pulling or pushing.
2. Discussion of Background Information
In known locks, the bolt slides in the opening plane by compressing a return spring when an action is exerted against the door.
To oppose the opening of the door, these locks are provided with a locking device preventing the bolt from sliding backward. The device is made of a movable mechanical member that prevents the bolt from sliding back in the locking position.
In general, the movable mechanical locking member is controlled by an electromagnet which, when energized, maintains the aforementioned member in the locking position. If the electromagnet is no longer energized, the aforementioned member retracts by means of a return spring.
Such a lock cannot be used in the case of a door which, while being maintained closed, must be openable, should fortuitous event, such as a fire alarm, occur.
The occurrence of such an event triggers the opening of the electrical circuits, either automatically, or by the security staff.
In general, the alarm trigger causes a panic situation, whereby a large number of people exert an action on the door (an emergency exit, for example), which results in each door being suddenly subjected to a substantial force, and the moving parts (bolt and movable locking member) being blocked one against the other. Experience has shown that a power shut-off has no effect because the force of the return spring is much too insufficient to overcome the force pressing the movable members against one another.
The solution would be to interrupt the power supply as soon as an ill-timed event occurs; but here again, experience has shown that this synchronization is very difficult to achieve.